AAS Nova

Selections from 2024: Mapping Quasars Across the Universe

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artist's impression of a quasar
Artist's impression of a luminous quasar surrounded by a swirling accretion disk. [ESA/Hubble, NASA, M. Kornmesser; CC BY 4.0]

Editor’s Note: For the remainder of 2024, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume January 3rd.

Quaia, the Gaia-unWISE Quasar Catalog: An All-Sky Spectroscopic Quasar Sample

Published March 2024

Main takeaway:

map of quasars in the Quaia catalog

The on-sky distribution of quasars in the Quaia catalog. The dearth of objects across the center of the image is due to the Milky Way’s disk. The team also developed a more refined sample of 755,850 quasars with especially reliable distance estimates. Click to enlarge. [Adapted from Storey-Fisher et al. 2024]

Beginning with 6,649,162 quasar candidates identified by the Gaia mission, Kate Storey-Fisher (New York University) and collaborators have constructed a catalog of 1,295,502 quasars spread across the sky. The catalog, named Quaia, includes redshifts for each quasar, enabling detailed studies of the large-scale structure of our universe over the course of cosmic history.

Why it’s interesting:

Quasars — short for “quasi-stellar radio sources” — are extremely luminous galactic centers powered by accreting supermassive black holes. Quasars are thought to reside in regions of dense dark matter, making them important probes of the unseen dark-matter structures that suffuse the universe. In addition to their cosmological importance, studying quasars can also clue us in to the physics of accretion, the growth of supermassive black holes, and the evolution of massive galaxies.

More details about the data:

The Gaia satellite, which began its mission in 2013, was designed to obtain precise positions, distances, and velocities for stars in the Milky Way. Fortuitously, Gaia also studiously documented its observations of objects that are far brighter and more distant than stars in our galaxy, like quasars. The initial 6.6-million-object sample of quasar candidates, however, was riddled with objects mistaken for quasars, and many of the distances to the objects — critical for cosmological studies — were wildly inaccurate. Storey-Fisher’s team incorporated data from other sources, like the Wide-field Infrared Survey Explorer and the Sloan Digital Sky Survey, to boost the purity of the sample and provide better distance estimates. You can explore the final sample for yourself at this link.

Citation

Kate Storey-Fisher et al 2024 ApJ 964 69. doi:10.3847/1538-4357/ad1328